Sensation and Perception is the seventh program in the DISCOVERING PSYCHOLOGY series. This program unravels the complex process of how we see. You'll learn about visual illusions and what causes them, the biology of perception, the visual pathway, and how the human brain processes information during perception.

Interview Excerpt: David Hubel and the Visual Pathway

Dr. David Hubel explains how cellular structures in the nervous system create the visual pathway between eyesight and brain processing.

In order to understand what we mean by pathway, you need to understand that cells are clustered in the nervous system. They're aggregated into groups the size of a grain of rice or a marble. One region is connected to another by cables.

So in the case of the visual pathway, you start with the retina where rods and cones are connected by cells. The output is the optic nerve, which contains a million fibers. They end up in one of two regions in the brain, and they connect to other regions, or to the many regions in the cortex. This whole trail is the pathway.

Our studies of single cells tell us that the pathway consists of at least three separate sub-pathways, each with a specific role: one is concerned with color, a second, with form, and a third with movement and depth. If we record any individual cell, depending on the channel, the cell will only respond to one of these three areas.

I want to see how individual cells work when we perceive. We've only studied a couple of the visual areas intensely, and there seem to be 18 to 24 different visual areas in the occipital lobe at the back of the brain. Most of our work is on the primary visual cortex, just the first of these areas. It's exceedingly complex, but we'll know more about all of the sensory pathways in the brain with more research and experimenting.

The 1981 Nobel Prize in Physiology or Medicine was awarded one half to Roger W. Sperry, for his discovery of the functional specialization of the cerebral hemispheres, and the other half jointly to David H. Hubel and Torsten N. Wiesel for their work concerning the visual system. Read the press release on the Nobel Prize Commission Web site describing their research. http://www.nobel.se/medicine/laureates/1981/press.html.